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I got what I thought were onion sets from a local nursery. I believe they are the brand Bonnie Plants. I think I got 2 varieties .... but they all look the same. They are supposed to be yellow onions, not green ones. When I planted them last week, they looked like this:

Does that look right? Are these really going to grow into large yellow onions???

Your onions look more like onion plants to me, rather than onion sets. Plants come in a bunch as little plants with the green tops already growing, while sets look like very small, dry onions that haven't yet sprouted tops.

Your plants appear to have yellow "skins" around the base. I planted red onion plants, and mine look red at the bottom. White plants have white skins. The stems and leaves look the same on all colors of onion plants, only the thin skins around the base show color.

When the onions first start growing and the leaves turn green you can pull a few for green onions if you wish. If you leave them to grow, eventually the bases will begin to swell and make large onions. I've been told that when the number of hours of sunlight in a day reaches a certain point, that is the signal for the bases to stop growing. The tops begin to die, and it will soon be time to harvest them.

Onions with thick necks do not keep well, so if you plan to pull any for green onions, choose those with the thickest necks, or any that put up seed stalks to eat first.